What is unbuffered memory?

superk

so I checked a RAM upgrade for my computer, and here it is:

Memory upgrades from Crucial.com - Determine My Memory Needs

the 8 GB module listed here is the upgrade in question. The listing refers to it as 'unbuffered'. What is this referring to, and what is the difference between 'unbuffered' RAM and the alternative? (buffered memory?) thanks!

EDIT: that link may be for the system scanner, scanning your computer....this is the link to the page dedicated to the RAM module I'm referring to....

http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=F12BF7A6A5CA7304

403Forbidden

Fully buffered memory takes some of the functions of the memory controller (a chip that controls the data flow of RAM) and puts it on the memory module. This increases memory scalability further. Fully buffered memory cannot be used in a computer that takes registered memory or vise versa. Fully buffered memory includes ECC functionality but not all ECC is fully buffered.
Unbuffered memory is memory that does not include any buffers or registers. It is the memory most commonly used in desktop and notebook computers. You cannot use registered memory or fully buffered memory in a computer that takes unbuffered memory.